Commentary for Berakhot 44:12

THE HALAKHA IS NOT IN ACCORDANCE WITH HIS [OPINION]. The Gemara related that Rav Chomo immersed himself in a mikvoh of forty s’ah on erev pesach before he would recite the Hagodoh for others. (It was the custom that only the leader of the seder said the Hagodoh, the others fulfilled their obligation by listening to him, via the process of - listening is the equivalent of saying.) Obviously he holds that when he is learning Torah himself it is not required to immerse in a mikvoh, rather pouring nine kav of water upon a person is sufficient. The Gemara concludes that the halochoh is not in accordance with Rav Chomo. Tosfos explores exactly which facet of Rav Chomo’s is not in accordance with the halochoh. The halochoho is not that immersion every day¹There is some difficulty with the text of the Tosfos. On the surface it appears that Rav Chomo require immersion when one is a baal keri on any day in forty s’ah. From the Gemara it would seem that the opposite is true. Rav Chomo himself immersed in a mikvoh of forty s’ah only erev pesach. When Tosfos uses the words אלא אפילו לאחרים, it seems that Tosfos had previously been speaking about requiring immersion in forty s'ah, when immersing in order to recite Torah for others. This concurs with our text of the Gemara. must be in a mikvoh of forty s’ah, rather even when one wants to recite words of Torah for the benefit of others it is sufficient to use nine kav.
According to this understanding we are only rejecting the special stringency of immersing in a mikvoh of forty s’ah, when reciting Torah for others. The enactment that one must use at least nine kav of water remains in full force. Alternatively, this is the explanation, and the halochoh is not like him, Rav Chomo, rather like R’ Yehudoh B’ Bsairoh who says that words of Torah do not become tomay and there is no need for any washing whatsoever, even nine kav.
According to this understanding the Gemara is ruling that the enactment of Ezra is not in effect at all. There are those who say that there is a remnant of Ezra’s enactment. And there are those who say that it is exclusively for Torah learning, that we say the enactment of Ezra is no longer in effect, but for praying, immersion is required. And the R’I explained that there is no difference and for prayer as well, immersion is not required.
Tosfos now examines a custom that was prevalent in his times. And one who immerses himself on Erev Yom Kipur²The Tur cites this custom and says it is based on Pirkay d’R’ Eliezer, who says that on Yom Kipur we must be pure as the ministering angels. It has therefore become the custom to immerse one's self Erev Yom Kipur. should not recite a blessing. And one who does recite a blessing, the b’rocho is in vain.

In forty Saot, because he used then to teach Torah ; but on other days, when studying for himself, be poured nine Kabs over himself.

I.e. either nine Kabs suffice even to teach, or as R. Judah b. Batyra said, "Words of Torah do not contract defilement " and no purification is necessary.